The table below summarises the plug types, voltage and frequency of electrical current in both Cook Islands and Estonia.
|Frequency of electrical current||50Hz||50Hz|
Cook Islands uses Plug Type I.
You will need this adaptor:
Socket Type I
(Cook Islands) to Plug Type F
The voltages found in Cook Islands (240V) and Estonia (230V) are not exactly the same, but the difference is tolerable, so you should not need a transformer.
The frequency found in Cook Islands and Estonia is exactly the same (50Hz). Timing devices and appliances that use motors will function as expected under this frequency.